The invention relates in general to direct tension indicating washers and in particular to direct tension indicating washers that indicate when the proper bolt tension has been achieved.
Direct tension indicating (DTI) washers are used in the art to indicate when proper bolt tension has been reached. U.S. Pat. No. 5,931,618, the entire contents of which are incorporated herein by reference, discloses an exemplary DTI. FIG. 1 is a top view of the DTI from U.S. Pat. No. 5,931,618. A direct tension indicating washer 60 includes protuberances 12 formed on a first surface 14 and corresponding indentations 16 formed on a second surface 18. The direct tension indicating washer 60 also includes channels 62 that lead from each indentation 16 to the outer diameter of the direct tension indicating washer 60. The indentation 16 is filled with an indicating material 64. The direct tension indicating washer 60 is manufactured using a tool and die to stamp the protuberances 12, indentations 16 and channels 62 into a blank washer. Other processes, such as metal machining or metal casting may be used to form the direct tension indicating washer 60. Direct tension indicating washer 60 is made from carbon steel, but stainless steel, nonferrous metals, and other alloy products may also be used. The indicating material 64 is an extrudable, elastomeric solid material such as colored silicone. FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1. FIG. 3 illustrates the protuberances before installation and after installation illustrating the compression of a protuberance 12, which forces indicating material 64 out channel 62 to the periphery of the direct tension indicating washer 60.
While the direct tension indicating washer of FIGS. 1-3 is well suited for its intended purposes, it has been discovered that a more prominent exodus of indicating material 64 from channel 62 is desirable. Pending U.S. patent application Ser. No. 11/875,224, the entire contents of which are incorporated herein by reference, discloses a direct tension indicating washer having a modified indicating material to provide a more prominent exodus of indicating material (also referred to as a “squirt event”). While this design is well suited for its intended purpose, there is a need to further improve the exodus of indicating material from the channel.